This invention relates to electronic identification systems including an interrogator and a plurality of transponders. The invention more particularly relates to interrogators or readers forming part of such systems, especially radio frequency (RF) identification systems.
Known electronic identification systems of the aforementioned kind include a reader including a transmitter for transmitting an energizing field or interrogation signal to the transponders; and a receiver for receiving a response signal from the transponders. A microprocessor in the reader identifies a particular transponder by identification code data unique to the transponder forming part of a backscattered response signal. Upon receipt of the identification code data by the reader and thus upon identification of the transponder, the reader transmits an acknowledgement signal to the transponder to switch the transponder to a catnap mode wherein it stops responding to the interrogation signal, while still being energized. After the energizing signal has been removed from the transponder for a period longer than a reset period (typically shorter than two seconds), the transponder reverts to a normal operational mode wherein it responds as hereinbefore described with identification code data upon being energized.
In applications where a large number of transponders mounted on articles to be identified need to be read, it may be necessary to scan the energizing field over the articles. Due to scattering and reflections of the energy, a remote transponder not yet in the field, may be energized and thus read as hereinbefore described. However, as the field is moved, the scattered energy is also removed from the transponder just read, so that the transponder will switch from the catnap mode to the normal operational mode. When the actual energizing field later illuminates that transponder, that transponder will be read a second time, resulting in errors in the data read and recorded.
Accordingly it is an object of the present invention to provide a apparatus and a method with which the applicant believes the aforementioned disadvantages may at least be alleviated.
According to the invention there is provided a reader arrangement for an electronic identification system, the reader arrangement including a plurality of reader heads for energizing transponders to be read; and control means for time multiplexing activation of the reader heads.
The activation may be multiplexed by switching activation of the reader heads in a multi-phase sequential pattern including a first phase for activating a first set of the reader heads and at east one further phase for activating at least one further set of said reader heads, so that a complete cycle plus at least the first phase of a subsequent cycle is completed within a time period not longer than a reset period of the transponders, the reset period being the period between removal of an energizing signal from a transponder and the transponder re-entering a normal operational mode.
The reader heads may be arranged in an array, such as a linear array or a rectangular array.
The reader heads in the first set and the reader heads in the at least one further set may be arranged in alternating relationship, so that radiation patterns associated with simultaneously activated heads do not overlap.
The arrangement may be stationary. In other embodiments at least the reader heads may be moveable past a volume including transponders to be read.
The reader arrangement may include a central reader and the control means may include fast switching switch means, for example PIN diodes, for connecting the heads to the central reader in the multi-phase sequence. Where a set comprises more than one reader head, the reader heads of that set may be connected to the reader via a power splitter arrangement.
In some embodiments, multiple reader arrays may be utilized and in such embodiments adjacent heads in neighbouring arrays are controlled such that they are not activated simultaneously.
The arrangement may further include at least one energizing means including at least one energizing signal transmitter for preventing the transponders from exiting the catnap mode and thus resetting to a normal operational mode of the transponder.
In some of these embodiments the reader head array may be positioned between a leading energizing array and a trailing energizing array.
At least some of the heads may be arranged such that central axes of radiation patterns associated with the heads extend transversely relative to one another. The axes may for example extend perpendicular relative to one another.
Each head may include an antenna adapted to transmit or receive signals the polarization of which is not limited to one plane.
Also included within the scope of the present invention is a reader arrangement for an electronic identification system including a plurality of reader heads, each head being associated with a radiation pattern wherein it transmits an energizing signal for energizing transponders; at least some of the heads being arranged such that the central axes of respective patterns extend substantially transversely relative to one another.
Yet further included within the scope of the invention is a reader arrangement for an electronic identification system including an antenna adapted to transmit or receive signals the polarization of which is not limited to one plane.
Still further included within the scope of the present invention is a reader head for an electronic identification system, the reader head including a plurality of energizing elements for energizing transponders to be read; and wherein the elements, in use, are activated in a time-division multiplexing manner.
The energizing elements may be first and second antenna elements arranged for transmitting or receiving signals polarized in first and second planes respectively and the elements may be activated by switching activation of the elements in a multi-phase sequential pattern including a first phase for activating the first element and a second phase for activating the second element, so that a complete cycle plus at least the first phase of a subsequent cycle is completed within a time period not longer than a reset period of the transponders, the reset period being the period between removal of an energizing signal from a transponder and the transponder reentering a normal operational mode.
Also included within the scope of the present invention is a method of reading a plurality of transponders including the steps of: providing a plurality of reader elements; and activating the elements in a time-division multiplexing manner, to energize the transponders.
Each transponder may be of a kind having an operational mode wherein it is responsive to energization by a reader by transmitting data to be received by the reader; and a catnap mode which the transponder enters after reception of the data has been acknowledged by the reader and wherein the transponder remains until energization is removed from the transponder, the transponder further being adapted to re-enter the operational mode a reset period after energization has been removed therefrom, the activating step may include the step of switching activation of the reader elements in a multi-phase sequential pattern comprising a first phase for activating a first set of said reader elements and at least one further phase for activating at least one further set of said reader elements, so that a complete cycle plus at least the first phase of a subsequent cycle is completed within a time period not longer than the reset period of the transponders.
The elements may form part of reader heads and in one embodiment of the method the reader heads may be kept stationary and may be arranged such that radiation patterns associated with the reader heads collectively cover a volume to be read.
In another embodiment, the method may include the steps of moving the reader heads past a volume to be read; and utilizing energizing means to keep transponders not in energizing fields associated with the reader heads in an operational mode, so that they are not affected by scattered energy originating from the reader heads and/or to keep transponders already read in the catnap mode.